In industrial equipment, the motor is the core component. Many see the motor core joining method as merely an “assembly detail,” yet it profoundly influences overall efficiency, service life, and energy consumption.

Why Are Motor Cores “Laminated in Layers”?

As devices that convert electrical energy into mechanical energy, motors are widely used in industrial equipment, such as electric vehicles, electric aircraft, and electric ships. Silicon steel, a high-silicon (2-5.5 wt% Si) thin strip (0.2-0.65 mm) steel, is the most common soft magnetic material used in motor stators and rotors. Adding silicon reduces coercivity and increases resistivity in the steel. Moreover, thinner strips reduce eddy current losses under alternating magnetic fields.

Motor stator and rotor cores are constructed from hundreds of laminated silicon steel sheets to minimise eddy current losses and improve efficiency. Each side of the laminated core is coated with insulation to block interlayer eddy currents. Typically, lamination aims to ensure mechanical strength, but joining processes may damage the insulation coating, alter microstructures, or introduce residual stress, all of which can degrade magnetic properties. Balancing mechanical strength and magnetic performance remains a significant challenge.

Additionally, the laminated structure of silicon steel differs from traditional overlap or butt-joint assemblies. Studying silicon steel lamination joining techniques is crucial for accelerating the production of high-quality motors.

MOOPEC focuses on supplying high-performance CRGO and CRNGO electrical steels for motor cores, offering advanced slitting, cut-to-length, and surface coating protection processes to ensure the magnetic stability and low-loss characteristics of laminated structures.

Representative Core Joining Techniques

Currently, laminated core joining techniques fall into three main categories: bonding, mechanical fastening, and fusion welding.

1. Bonding (Similar to Gluing)

Advantages: Does not damage insulation, low iron loss, quiet operation, good heat dissipation.
Disadvantages: High cost, adhesives may age under high temperatures.

Bonding offers great flexibility during manufacturing and can be used on cores with complex shapes. Various adhesives are available, including organic, inorganic, and hybrid types. Once cured, adhesives provide mechanical strength and thermal conductivity. However, under high load, high temperature, or high humidity conditions, durability remains a concern, and costs are generally higher than other joining techniques.

Schematic diagram of representative connection processes for laminated cores: 
(a) Adhesive connection (b) Mechanical connection (c) Fusion welding connection

2. Mechanical Fastening (Similar to Clamps or Rivets)

Advantages: Simple structure, low processing cost.
Disadvantages: Low strength, prone to loosening, magnetic performance degrades at high frequencies.

Mechanical fastening includes V-shaped clips, riveting, and locking tabs, suitable for mass production of low- to medium-power motors with lower strength requirements. These methods are often integrated with stamping tools, enabling high-efficiency joining on automated production lines. However, local damage to the insulation layer at connection points can reduce magnetic performance, so mechanical fastening is often combined with other methods.

3. Fusion Welding (High-Temperature Fusion)

Laser welding is currently the most promising technology—offering small weld seams, low residual stress, and minimal impact on magnetic properties. It is ideal for motors with high-performance requirements, such as electric vehicle drive systems.

Unlike traditional TIG or MIG welding, laser welding produces smaller heat-affected zones and finer weld boundaries, preserving both weld strength and magnetic properties. It is particularly suited for wound cores and precision small motors with complex structures or demanding performance requirements.

MOOPEC’s Nantong processing centre has introduced laser welding production lines capable of welding customised structures such as three-column or five-column cores, and provides end-to-end processing from material supply to lamination.

Schematic diagram of laser welding for laminated cores

Why Does Joining Method Matter So Much?

Joining the core isn’t just about “connecting pieces together.” Different methods affect material permeability, eddy current loss, and structural strength. For example:

• Bonding preserves insulation, resulting in the lowest iron loss, but adhesives may degrade over time.

• Mechanical fasteners offer lower stability and are prone to failure during long-term operation.

• Laser welding is the most ideal solution but requires high-precision equipment.

Moreover, the joining process itself introduces residual stresses, which can degrade magnetic performance under magnetic fields. Therefore, evaluating joining methods requires not only cost and process considerations but also a comprehensive analysis of their impact on electromagnetic performance.

In practice, hybrid approaches are often used. For example, some MOOPEC products combine bonding and laser welding to balance performance and strength without significantly increasing costs.

New Trends: Spot Welding, Pulse Welding & Intelligent Assembly

As the new energy sector evolves rapidly, performance requirements for motor cores are rising. Traditional large-area welding caused excessive heat, coarse grain structures, and degraded magnetic performance. Today, the industry favours “pulse spot welding”—using small, high-frequency energy bursts to weld multiple points quickly with minimal impact.

Research shows that spot welding performs better at low frequencies, while high-frequency applications require further optimisation of insulation treatments and weld density. To ensure consistent weld quality, modern manufacturing now incorporates “welding monitoring and control systems”, such as infrared temperature sensors and welding current waveform analysis.

MOOPEC is implementing intelligent data systems for quality tracking and parameter monitoring, and offers customised hollow core assembly services based on customer drawings—meeting the lamination needs of both standard and non-standard motor stators.

How to Evaluate Joining Quality?

Currently, evaluations focus on two main aspects:

• Mechanical testing: e.g., torsional strength and shear tests, measured using specialised equipment.

• Magnetic performance testing: e.g., measuring iron loss and flux density, assessed with standard instruments.

For more comprehensive data, research institutions often combine thermal analysis, finite element analysis (FEA), and digital image correlation to map stress distribution and strain migration in the weld heat-affected zones—optimising structural design and process parameters.

Some studies are even using thermal imaging and neutron grating techniques to further quantify weld effects, laying the groundwork for high-end equipment.

Future Trends: Smarter, More Efficient, More Flexible

Looking ahead, motor core joining techniques will evolve in the following directions:

• High-frequency laser welding gradually replacing traditional methods.

• Smart, traceable, and predictive joining processes.

• Customised and flexible small-batch lamination manufacturing.

• Data-driven process optimisation, self-learning parameters, and real-time adjustments.

These trends rely heavily on continuous technological investment and strong service systems.

MOOPEC is committed to building a complete “coil-to-core” solution, combining precision machining with flexible assembly to enhance the competitiveness of customers’ motor products.

MOOPEC – Your Partner in High-Performance Transformer Cores

MOOPEC is a technology-driven provider of electrical steel and core lamination services, offering end-to-end “coil-to-core” solutions tailored for transformer and motor manufacturers.

Our capabilities include:

Material sourcing for CRGO/CRNGO with multi-currency, small-batch trade support

Product Specifications

International CRGO Grades

References Core Loss Curves

Applications

Precision slitting, shearing, and professional step-lap/mitred lamination services

Based in Nantong, with advanced facilities including laser cutting and robotic stacking

Engineering support from drawing analysis to loss optimization and insulation strategies